A FPGA-based high speed multi-channel simultaneous signal acquisition method for PET

A PET data acquisition (DAQ) system based on multiple high-speed, 8-channel DAQ cards is being developed. Each of these DAQ cards has 8-channel 14-bit 100 MHz simultaneous ADCs, a six million-gate FPGA with 104 MHz onboard clock and a 16-bit 128 MB SDRAM. The SDRAM has a data transfer bandwidth of 450 MB/S, thus for raw data acquisition, only two channel ADCs can be simultaneously used at sampling rate of 100 MHz (for 8 channel simultaneous acquisition, the maximum sampling rate is about 28 MHz). In this study, data packages containing pulse arrival time, baseline, energy and position were saved instead of raw data of whole gamma signal pulse to reduce the amount of output data. Parallel signal processing containing arrival time detection, baseline calculation, pulse energy calculation and channel ID generation were implemented by model-based design method to achieve high performance PET signal processing. Finally, data packaging and down sampling approaches were employed to achieve 8-channel simultaneous signal acquisition at 100 MHz sampling rate without exceeding the SDRAM data transfer bandwidth. To examine the functionality of the signal acquisition method, PET images were obtained using a pair of detectors. The PET detector is composed of a Geiger mode avalanche photodiode (GAPD) array (3 mm × 3 mm, 4×4) coupled with LYSO array crystal (3 mm × 3 mm × 20 mm, 4 × 4). By rotating a pair of PET detectors for 180 degrees (6 degrees × 30 times) and simultaneously acquiring 8 channel (4 channels from each GAPD array) signals using one acquisition card, PET images of two F-18 line sources were successfully acquired. The energy resolution for 8-channel gamma signals was 19% and the timing resolution for the coincidence channels was 1.5 ns. The spatial resolution for the acquired PET image was 3.1 mm. Finally, a brain PET system using three DAQ cards has been developed and high quality PET images were acquired.